Let \(y\) varies directly as \(x\). If \(y\) \(=\) 12 when \(x\) \(=\) 3, then write a linear equation. What is the value of \(y\) when \(x\) \(=\) 13?
 
Linear equation \(=\)
 
The value of \(y\), when \(x\) \(=\) 13 is .